# Binding Generation

Understanding and using type-safe client code for calling canisters.

## What Are Bindings?

Bindings are generated code that provides type-safe access to canister methods. They're created from Candid interface files (`.did`), which define a canister's public API.

## Candid Interface Files

Candid is the interface description language for the Internet Computer. A `.did` file defines the public methods and types a canister exposes — it's the contract between a canister and its callers.

`.did` files can be:
- **Manually authored** — Recommended for stable APIs where backward compatibility matters
- **Generated from code** — Convenient during development, but review before publishing

For Candid syntax and best practices, see the [Candid specification](https://github.com/dfinity/candid/blob/master/spec/Candid.md).

## Generating Client Bindings

icp-cli focuses on deployment — use these dedicated tools to generate bindings:

| Language | Tool | Documentation |
|----------|------|---------------|
| TypeScript/JavaScript | `@icp-sdk/bindgen` | [js.icp.build/bindgen](https://js.icp.build/bindgen) |
| Rust | `candid` crate | [docs.rs/candid](https://docs.rs/candid) |
| Other languages | `didc` CLI | [github.com/dfinity/candid](https://github.com/dfinity/candid) |

> **Note:** Generated bindings typically hardcode a canister ID or require one at initialization. With icp-cli, canister IDs differ between environments. You can look up IDs with `icp canister status <name> -i`, or read them from canister environment variables at runtime. See [Canister Discovery](canister-discovery.md) for details.

### TypeScript/JavaScript

Use `@icp-sdk/bindgen` to generate TypeScript bindings from Candid files. See the [@icp-sdk/bindgen documentation](https://js.icp.build/bindgen) for usage and build tool integration.

### Rust

The `candid` crate provides Candid serialization and code generation macros. See the [candid crate documentation](https://docs.rs/candid).

### Other Languages

The `didc` CLI generates bindings for various languages. See the [Candid repository](https://github.com/dfinity/candid) for available targets.

## See Also

- [Canister Discovery](canister-discovery.md) — How canisters find each other's IDs
- [Local Development](../guides/local-development.md) — Development workflow

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